Myelination will be studied using primary cultures, purified oligodendroglia, and clonal lines exhibiting characteristics of oligodendroglia or Schwann cells. Following the onset and attainable levels of expression of a limited number of myelin-associated biochemical phenomena, especially the syntheses of myelin basic protein, proteolipid protein, and the levels of activity of 2', 3'-CpNase and cholesterol ester hydrolase, these studies will attempt to better define the environmental factors controlling myelinogenesis. These include the importance of extracellular matrix-cell and glial-neuronal interactions, exogenously-supplied hormones and growth fators, and metabolic precursors.